Bearings are a very important component in rotating machinery. If a bearing fails, then the complete functionality of the machinery usually also fails. In some applications it might be very difficult or just extremely expensive to replace a failed bearing outside regular scheduled maintenance. Such applications might be deep sea applications, cruise ships or other continuous manufacturing lines. In an attempt to predict when a bearing needs to be replace before it fails and suitable also in an orderly scheduled manner, condition monitoring is done. If the machinery and bearings are physically in a location which is easily accessible, then the condition of a bearing can be assessed by for example vibration measurement. Equipment which is not accessible, such as deep sea applications need other means to assess the condition of a bearing to be able to assess when maintenance is needed. There are many ways of remotely assess the condition of a bearing, however, there seems to still be room for improvement.